This invention concerns a device for the support and movement of workpieces, assembly parts, or the like, by a stepping transmission having a click-stop setting are located in a gearbox, which controls two reciprocal motions of the workpiece through cam plates fastened to a drive shaft. Included as a first motion is that of a carriage sliding on the gearbox housing, and, as a second motion, that of a holder guided on the carriage essentially perpendicularly to the first motion.
Such devices are used for the automatic removal, replacement, and transporting of assembly parts, for loading workpieces into machine tools, and for like operations. For this purpose, an appropriate tool to grip the workpiece or the assembly part is fastened to the holder. The cycle of motion of the holder with the tool in this case generally consists of, lifting, forward motion, lowering, and subsequent retraction of the holder. Depending on the arrangement of the cam plates on the drive shaft, this retraction can be brought about immediately or after a lowering of the holder. Optionally another lifting may follow the setting down of the workpiece or assembly part; in this case, another lowering follows the retraction in order to return to the click-stop position.
In a known device of this design (shown in Mink U.S. Pat. No. 4,002,245), a cam plate is provided on the drive shaft for the control of the carriage, and another cam plate is provided for the control of the holder. The operation occurs in each case through a lever, whose shorter lever arm is held in position at the circumference of the associated cam plate by means of spring force at its free end which has a roller, and whose longer lever arm brings about the reciprocal motion through a rocker arm guide. An unfavorable transmission results from this. In addition, a tightening of the available manufacturing tolerances, from which will follow increasing inaccuracy with increasing wear between the cam plate and the roller of the lever, since this inaccuracy of the holder motion is not only amplified with increasing wear, but furthermore becomes larger from the outset as a result of the unfavorable lever transmission. The consistency of the center position and the reproducibility of millimeter-precision motions therefore leaves something to be desired. Furthermore, because of the spring action which is intended to hold the shorter lever with its roller in position on the cam plate, the cadence or the number of operating cycles per unit time cannot be arbitrarily high, since a transient lifting of the roller from the circumference of the cam plate can occur because of the accelerations appearing, in spite of the opposition of the spring, which can lead to jerky motions during the stroke and also to inaccuracies. Finally, this known stepping transmission is a so-called swing transmission with a maximum swing angle of only 45.degree., which makes possible undesirable elastic deformations in tension or compression in the end positions, which also bring about inaccuracies.
The use of complementary cam plates for stepping transmissions is known from German Patent No. 2,903,732. It is also understood that crank-coupling transmissions are known in themselves.
The problem which the invention addresses is considered to be the provision of a device of the type described initially which provides a high cadence and more precise reproducibility of the desired motion cycles at the same time, while avoiding the drawbacks mentioned.